1. Field of the Invention
The present invention relates generally to arc-quenching compositions and articles formed therefrom and more particularly to a fuse tube construction which is easily manufactured utilizing inexpensive materials and that exhibits excellent strength and arc-quenching properties for operation over a wide range of currents.
2. Description of the Related Art
Fuse tubes for medium and high-voltage electrical fuses wherein circuit interruption takes place within the fuse tube requires high strength and arc-quenching properties. Examples of prior art fuse tubes are found in U.S. Pat. Nos. 3,911,385, 3,979,709, 3,984,800, 4,313,100, 4,349,803, 4,373,555, 4,373,556, 4,564,830, 4,808,963, 5,015,514 and 5,119,060. Fuse tubes for operation to interrupt currents over a wide range, e.g. 100-10,000 amperes, require especially high strength and arc-quenching properties that are difficult to obtain. In conventional fuse cutouts utilized in electrical power distribution systems, the fuse tube is fabricated by winding a filament-wound glass-epoxy outer tube over an inner tube of vulcanized fiber that provides the arc-quenching properties. Various alternatives have been proposed to fabricate fuse tubes with overall high strength and a bore of suitable arc-quenching properties. Some of these alternatives include various fabrication techniques utilizing fiber supported in epoxy resin mixtures to provide an inner layer having arc-quenching properties over which is formed an outer layer providing strength. In the aforementioned U.S. Pat. Nos. 4,373,555 and 4,373,556, the inner arc-quenching layer of the fuse tube is fabricated from polyester fiber and epoxy resin mixture. In U.S. Pat. No. 5,015,514, approximately 55-60% aluminum trihydrate is included by weight in an inner arc-quenching layer along with organic fiber and epoxy resin. In the aforementioned U.S. Pat. No. 4,349,803, a molded tube includes a layer of porous fiberglass cloth with an inner layer of thermosetting material having an arc-quenching material therein and an outer weather resistant portion being formed about the intermediate porous fiberglass cloth.
While the prior art arrangements may be generally useful to provide fuse tubes for electrical fuses, the prior arrangements involve either relatively expensive natural resources or complex processing and fabrication. Further, most do not provide a fuse tube which is capable of withstanding the pressures of high-current interruptions and also being capable of interrupting low current faults.
Accordingly, it is a principal object of the present invention to provide an arc-quenching composition that is useful for forming articles thereof and particularly the inner arc-quenching layer of a high-strength layered fuse tube.
It is another object of the present invention to provide a fuse tube for electrical fuses that exhibits excellent strength and arc-quenching characteristics while also being easily fabricated from resins, fiber and fillers.
It is a further object of the present invention to provide a fuse tube which is fabricated by forming an inner tube having a bore with arc-quenching properties and before the curing of the inner tube forming an outer tube over the inner tube such that the inner and outer tubes cure as a single structure and avoid any dielectric joint or interface therebetween.
It is yet another object of the present invention to provide an arc-quenching bore for a fuse tube that is capable of interrupting a wide range of currents via the combination of an arc-quenching compound in the bore and a predetermined taper in the bore.
These and other objects of the present invention are efficiently achieved by the provision of an arc-quenching composition including a filler, a fiber and a binder. Preferably, the filler includes an arc-quenching compound such as melamine. The binder includes a thermosetting resin to facilitate forming of the arc-quenching composition into an arc-quenching fuse tube. In a preferred arrangement, an outer tube is formed over the arc-quenching fuse tube to provide an overall high-strength fuse tube. Also in a preferred arrangement, in order to provide a fuse tube that is capable of operation over an extremely wide current range, the inner arc-quenching tube includes a tapered bore. According to one fabrication technique, the outer tube is formed over the arc-quenching inner tube before the curing of the inner tube such that a single structure results.